Electrical transmission line coupling structure



y 1967 D- N. SEWELL ETAL 3,322,444

ELECTRICAL TRANSMISSION LINE COUPLING STRUCTURE Original Filed May 21, 1965. 2 Sheets-Sheet 1 y 1 D. N. SEWELL ETAL 3,322,444

ELECTRICAL TRANSMISSION LINE COUPLING STRUCTURE Original Filed May 21, 1965 2 Sheets-Sheet 2 7m 3 60 FIGS FIG? United States Patent G tion of Michigan Continuation of application Ser. No. 461,591, May 21, 1965. This application June 9, 1966, Ser. No. 556,525

7 Claims. (Cl. 285-352) This application is a continuation of application Ser. No. 461,591, filed May 21, 1965, and now abandoned, which in turn is a continuation-in-part of our pending application, Ser. No. 217,622, filed Aug. 7, 1962 and now abandoned.

This invention relates to electrical transmission lines and more particularly to coupling structures especially adapted for sections of tubing such as waveguide or coaxial cable which function as electrical transmission lines.

In the coupling of sections of rectangular or circular electrical transmission line, the abutting ends of the sections should match uniformly so that the radio frequency currents that flow in or on the walls of the waveguide may be efficiently conducted across the joint and the energy leakage nad impedance mismatch will be minimized at that point. The joints between sections are generally the limiting factor in runs of waveguide because of the interruptions in the guide wall that they create. In recent years it has been necessary to pressurize the transmission line to prevent electrical breakdown of the dielectric where the system is operating at high power as, for example, in radar equipment and such operation dictates a joint must be capable of being sealed while maintaining good electrical characteristics. Many different coupling arrangements have been proposed. A commonly used arrangement employs a metallic plate which carries gaskets on either side thereof and is inserted between the flange of two waveguide sections to be coupled. In addition to a slight increase in the overall length of the waveguide run, such an arrangement introduces double the number of joints and the places to seal, and also increases the inventory problem in that such a supply of such gasket structures must be available for necessary maintenance.

Accordingly, it is an object of this invention to provide an improved electrical transmission line coupling device.

Another object of the invention is to provide an improved coupling device particularly suitable for use in pressurized waveguide tubes of electrical transmission lines.

Another object of the invention is to provide a simple and economical joint construction for electrical transmission lines which insures a pressure tight joint between line sections that has good electrical characteristics.

In accordance with the invention, a transmission line section of uniform diameter over its entire length has an end surface adapted to abut a similar end surface of an adjacent section. A flange plate encircles the section adjacent the end surface and its inner edge is welded to the outer wall of the section such that the transmission line and surface protrudes axially beyond the inner edge of the flange plate. This flange plate has a lip portion at its periphery that is accurately machined to lie in the same plane as the protruding end surface of the transmission line section. An intermediate portion of the flange between the lip portion and the transmission line adjacent the transmission line section wall has formed therein a channel that extends entirely around the transmission line section. This channel preferably has a depth greater than one-half the width of the channel and may have a ridge formed in the base thereof. An O-ring having a diameter slightly greater than the width of the channel is seated within the channel so that it is frictionally secured therein. The surface of the O-ring protrudes above the plane of the machined outer flange lip and the transmission line end surface. A similarly formed flange is secured to the transmission line section to be joined and an O-ring is seated in the channel of that flange. The two flanges are bolted together in conventional manner so that the two O-rings are compressed against one another in sealing relation with the machined end surfaces of the two adjacent transmission line sections in abutting contact so that a joint having excellent electrical transmission characteristics is provided. This assembly provides a compact, easy to assemble unit (in which no intermediate sealing member or gasket is employed), which unit is relatively simple to manufacture and insures excellent sealing characteristics for pressurized operation of waveguide and similar types of electrical transmission lines.

Other objects, features and advantages of the invention will be seen as the following description of a preferred embodiment thereof progresses, in conjunction with the drawings, in which:

FIG. 1 is a perspective view of two sections of waveguide and associated flanges constructed in accordance with the invention;

FIG. 2 is a perspective view of a portion of a flange constructed in accordance with the invention prior to Welding and machining operations;

FIG. 3 is a perspective view through the transmission line section and a section of the flange showing the relation of the flange to the waveguide after welding and machining but prior to molding operations;

FIG. 4 is a sectional view thnough the flange and waveguide wall showing the configuration of the molded channel defining structure;

FIG. 5 is a sectional view through the waveguide joint with the two waveguide sections in joined relation;

FIG. 6 is a plan view of a second form of flange constructed in accordance with the invention;

FIG. 7 is a sectional view taken along the line 7-7 of FIG. 6; and

FIG. 8 is a sectional view of a waveguide assembly joint employing the flange shown in FIG. 6.

A run of transmission line of the type to which the present invention is applicable may be made up of several coupled sections. Two of the sections 10, 12 to be joined are shown in FIG. 1. Secured to each section at the end thereof is a flange 14, 16 having hole 18 through which bolts are passed to secure the two flanges together with the end surfaces 20 of the Waveguide sections abutting. The flange is machined so that a continuous lip portion 22 at the outer periphery of each flange is aligned with the corresponding waveguide end surface 20 so that the two lip portions also abut when the flanges are secured together. Each flange is secured to the waveguide section by means of a weld 24 shown on the rear flange surface remote from the waveguide end surface 20. As such waveguide runs are normally operated under a pressure in the order of three p.s.i. with a controlled atmosphere of a fluid such as dry air, nitrogen or sulphur hexafluoride to insure the uniformity and integrity of the dielectric therein an adequate seal must be provided to prevent the escape of the pressurized medium. In the practice of this invention seals are designed to be capable of withstanding pressures in the order of sixty psi. and above. This seal is provided by an endless strip of resilient material, in the form of an O-ring 26, for example, which is secured in a seating channel formed in a molded sealing comaeaaaea position disposed in the junction between the waveguide and the inner periphery of the flange. This molded sealing composition, in addition to forming the O-ring receiving channel, provides an impervious seal immediately adjacent the weld area and thus eliminates a possible leakage path in that area.

A portion of the flange structure as cast is shown in FIG. 2. As indicated in that figure, the flange has an inner wall 32 which is machined to conform relatively closely to the outer peripheral wall of the waveguide section so that it will slide smoothly over that surface. Irnmediately adjacent the inner wall 32 there is a recess 34 that extends entirely around the flange. To the outside of the recess is a section 36 in which bolt holes and flange alignment holes are machined and at the outer periphery of the flange is a raised surface or lip portion 38 which also extends entirely around the flange.

In assembly this flange is positioned on a conventionally formed section of waveguide perpendicular to the major axis of the waveguide. The recess 34 is immediately adjacent the outer wall of the waveguide. The flange is welded in position with a continuous weld bead 24 to secure the flange and waveguide together as a structural unit.

After the welding of the flange to the waveguide section, the raised lip surface 38 of the flange and waveguide end surface 20 are finished to a fine machined surface. The lip 38 and the end surface 20 are of uniform height and lie in the same plane. Bolt holes 18 are also bored to enable two flanges and the associated waveguide sections to be coupled together.

A molding die 44 (coated with a suitable release agent such as tetrafluoroethylene polymer (Teflon)) is clamped against the machined end of the fabricated flange and waveguide to form a cavity adjacent the recess 34. A plastic sealing material, such as an aluminum filled epoxy resin of the type manufactured by Devcon Corp, is then injected into this cavity to fill the recess 34 and any gaps or voids that may exist between the flange and waveguide wall adjacent recess 34. In many cases there are small spaces between the flange and the adjacent surface of the waveguide and there may be minor voids through the weld. In addition, there are often fairly large gaps at the corners of the waveguide. The sealing composition supplements the structural weld and firmly adheres to the metallic surfaces. The characteristics of the composition are such that the molded structure can be cycled over a range of temperature from 60 to -|230 F. without impairment in the quality of the seal between the flange and the waveguide. In addition to forming a waveguide flange seal, the composition is also molded to form a channel 48 for receiving an O-ring 26. This channel has a depth D which is in excess of one half the width W of the channel so that an O-ring 26 of diameter slightly greater than W may be positively secured therein as indicated by the dotted lines in FIG. 4.

An assembled joint of the coupling device as shown in FIG. with the two O-rings 26, one carried by each molded channel, in abutting and compressed relation under the influence of the tightened down bolts 50. As the molded channel 48 is rigid compared to the resilient 0- rings 26, they are compressed and contact each other along a surface 52 of substantial width to provide a continuous seal around the entire periphery of the joint, which prevents a loss of pressurizing fluid from within the waveguide. The machined lip portions 33 and end surfaces 20 are drawn into firm metallic contact by the bolts so that the waveguide surfaces form a joint having excellent electrical transmission characteristics and the flange lip portions aid in assuring continuing accurate alignment and mechanical rigidity of the waveguide run providing positive control on the compresson of the O- ring seal.

A second embodiment of the invention is shown in FIGS. 68. In this embodiment a flange 60 is employed that has an inner peripheral surface 62 of a size to fit closely over the waveguide section to which it is to be welded. A lip 64 at the rear edge of the inner periphery is provided for locating the weld bead 66 (FIG. 8). The flange has a series of holes 70 for receiving clamping bolts.

In the front face of the flange at its outer periphery, there is provided an upstanding lip 72 which protrudes above the plane of the front surface. The transverse surface 74 of this lip is smoothly machined. Interposed between lip 72 and the inner peripheral surface, also in the front face, is a continuous channel '76 for receiving a continuous, shaped O-ring 78. This channel has a ridge centrally located in the base of the channel of width approximately one third the width of the channel. The width of the channel is greater than the depth of the channel from lip surface 74 to the top of ridge 80 so that the O-ring 78 when positioned in channel 76 protrudes above lip 72.

This flange is welded to a waveguide 82 as indicated in FIG. 8 so that its front face is the axially outer face. The weld bead 66 must be carefully made so that no through holes exist if the waveguide is to be pressured. In assembling the waveguide and flange, the end 86 of the guide protrudes beyond the front face of the flange. This end 86 is machined or otherwise positioned in exact alignment with surface 74 of lip 72. O-ring 78 is disposed in channel 76 so that it projects above the plane of lip surface 74 and waveguide end surface 86.

This assembly is positioned in alignment With a corresponding assembly as indicated in FIG. 8. Bolts 90 draw the corresponding flange lip surfaces 74 and the waveguide end surfaces into firm engagement so that direct electrical connection is made between the two end surfaces 86 of the waveguides. The aligned O-ring 78 are also compressed to form a tight seal with the ridge 80 forcing the center portions of the O-rings into firm sealing engagement while ample space for deformation of the O-ring is provided on either side of the ridges 80. Should a seal not be required, the Orings can be omitted without other modification of the assembly and the electrical signal transmission characteristics of the joint are in no degree impaired.

Thus it will be seen that the invention provides an improved coupling joint particularly useful on electrical transmission lines such as waveguides and coaxial lines. The joint does not require line elements to have unusual end configurations and standard line elements are merely cut and secured to the flanges. A plastic material may be employed in a recess in the flange immediately adjacent the outer wall of the transmission lines to fill small voids and/or seams that may exist between the flange and the waveguide and also to form a channel for receiving an endless resilient sealing element. This channel may also be formed directly in the metal flange. This joint structure minimize the amount of machining that is necessary and eliminates the necessity of machining any weld area. Further, excellent electrical contact between the transmission line end surfaces is provided. These couplings constructed in accordance with the invention have advantages over the presently employed systems as no allowance for a sealing insert such as a metal plate with sealing elements secure thereto is necessary and hence no overall waveguide run length compensation is required for the possibility of the waveguide being used in a pressurized system. Further, this coupling enables a substantial reduction in the number of electrical joints in such a system. This assembly provides an O-ring receiving channel in which the O-ring is positively secured but from which it may be easily removed for replacement if necessary. The machined waveguide end surfaces provide a joint of excellent electrical quality since contact is achieved substantially uniformly over the entire surface rather than at random points as at 75 bolts which are relatively remote from the guide walls themselves in combination with an aligning joint surface at a point radially spaced from the waveguide joint.

While particular embodiments of the invention have been shown and described, various modifications thereof will occur to those of ordinary skill in this art and therefore it is not intended that the invention be limited to the disclosed embodiments or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

We claim:

1. An electrical transmission line assembly comprising a pair of electrically conductive transmission line sections, each said section being of uniform cross-sectional configuration over its entire length,

a radially extending flange member positioned over each said transmission line section adjacent the end surface of the section in secured relation with the end of the transmission line section protruding a predetermined distance beyond the axially outer face of said flange member,

each said flange member having an inner peripheral surface of the same configuration as the outer peripheral surface of said transmission line section and an axially extending lip portion in the axially outer face of the flange member adjacent the outer periphery thereof,

said lip portion having an axially extending height equal to said predetermined distance,

each said flange member having a recess in its outer face adjacent its inner periphery that extends entirely around said transmission line section,

plastic material disposed in said recess and in the space between said flange and the outer surface of said transmission line section so that a fluid tight seal is provided between said flange and the outer surface of said transmission line section,

a channel formed in said plastic material adjacent the axially outer face of each said flange member adjacent the outer wall of the transmission line section and extending entirely around said transmission line section, each said channel being of the same dimensional configuration,

resilient sealing means disposed in each said channel with a portion of said resilient sealing means protruding above the plane defined by the axially outer surface of the lip portion and the end surface of the corresponding transmission line section,

and securing means acting on said flanges intermediate said transmission line sections and said lip portions to couple said flanges together and maintain said transmission line end surfaces and said lip portions respectively in contact with one another.

2. The coupling structure as claimed in claim 1 wherein said plastic material is a metal-filled epoxy resin.

3. An electrical transmission line assembly for transmitting radio frequency electrical energy comprising a pair of electrically conductive tubular transmission line sections, each said section being of uniform cross-sectional configuration over its entire length, and both of said sections being of the same cross-sectional configuration,

a radially extending flange member positioned over each said transmission line section adjacent the end surface of the section in secured relation with the end portion of the transmission line section protruding a predetermined distance beyond the axially outer face of said flange member, said protruding end portion being of the same cross-sectional configuration as the remainder of said section and being unsupported in the radially outward direction by said flange member,

each said flange member having an inner peripheral surface of substantially the same configuration as the outer peripheral surface of said transmission line section, a radially extending body portion, and an axially extending lip portion in the axially outer face of the flange member adjacent the outer periphery thereof that projects beyond said body portion,

said lip portion having an axially extending height substantially equal to said predetermined distance so that said lip portion and the end of said transmission line section lie in substantially the same plane, which plane is beyond the axially outer face of said body portion,

and securing means acting on said flange body portions intermediate said transmission line sections and said lip portions to couple said flanges together and maintain said transmission line end surfaces and said lip portions respectively in contact with one another so that a substantially continuous tubular section inner surface for the transmission of radio frequently electrical energy between said sections is provided.

4. The assembly as claimed in claim 3 and further including a channel in the axiallyouter face of the body portion of each said flange member adjacent the outer wall of the transmission line section and extending entirely around said transmission line section, each said channel being of the same dimensional configuration and adapted to receive resilient sealing means with a portion of said resilient sealing means protruding above the plane defined by the axially outer surface of the lip portion and the end surface of the corresponding transmission line section.

5. The assembly as claimed in claim 4 and further including resilient sealing means removably disposed in said channel with a portion thereof protruding above the plane defined by said lip portion surface and the end surface of said transmission line section so that said securing means acts to move said sealing means into compressive contact with corresponding sealing means carried by the juxtaposed flange to provide a fluid tight joint between said transmission line sections.

6. The apparatus as claimed in claim 5 wherein said resilient sealing means is an endless sealing member of circular cross-section that is frictionally secured in said channel.

7. The apparatus as claimed in claim 4 wherein each said channel has a uniform depth greater than one half its width and a ridge of width less than one-half the width of said channel in the base of said channel.

References Cited UNITED STATES PATENTS 1,045,389 11/1912 Gillmor 285-336 1,071,235 8/1913 Hutton 285-352 X 2,383,089 8/1945 Theiler 285-336 X FOREIGN PATENTS 531,153 8/1954 Belgium.

957,929 2/1957 Germany. 1,065,034 9/ 1959 Germany. 1,070,705 12/ 1959 Germany. 1,122,122 1/ 1962 Germany.

1,033 4/ 1871 Great Britain.

CARL W. TOMLIN, Primary Examiner. T. F. CALLAGHAN, Assistant Examiner. 

1. AN ELECTRICAL TRANSMISSION LINE ASSEMBLY COMPRISING A PAIR OF ELECTRICALLY CONDUCTIVE TRANSMISSION LINE SECTIONS, EACH SAID SECTION BEING OF UNIFORM CROSS-SECTIONAL CONFIGURATION OVER ITS ENTIRE LENGTH, A RADIALLY EXTENDING FLANGE MEMBER POSITIONED OVER EACH SAID TRANSMISSION LINE SECTION ADJACENT THE END SURFACE OF THE SECTION IN SECURED RELATION WITH THE END OF THE TRANSMISSION LINE SECTION PROTRUDING A PREDETERMINED DISTANCE BEYOND THE AXIALLY OUTER FACE OF SAID FLANGE MEMBER, EACH SAID FLANGE MEMBER HAVING AN INNER PERIPHERAL SURFACE OF THE SAME CONFIGURATION AS THE OUTER PERIPHERAL SURFACE OF SAID TRANSMISSION LINE SECTION AND AN AXIALLY EXTENDING LIP PORTION IN THE AXIALLY OUTER FACE OF THE FLANGE MEMBER ADJACENT THE OUTER PERIPHERY THEREOF, SAID LIP PORTION HAVING AN AXIALLY EXTENDING HEIGHT EQUAL TO SAID PREDETERMINED DISTANCE, EACH SAID FLANGE MEMBER HAVING A RECESS IN ITS OUTER FACE ADJACENT ITS INNER PERIPHERY THAT EXTENDS ENTIRELY AROUND SAID TRANSMISSION LINE SECTION, PLASTIC MATERIAL DISPOSED IN SAID RECESS AND IN THE SPACE BETWEEN SAID FLANGE AND THE OUTER SURFACE OF SAID 